The present invention relates generally to hitches for work vehicles such as agricultural tractors. More particularly, the invention relates to an improved rocker for such hitches that greatly facilitates mounting, removing and servicing of the hitch and its components. The invention also relates to a method for making the improved rocker as well as to a structure for mounting the rocker onto a vehicle.
In the art of hitch assemblies for tractors and other work vehicles, a variety of structures have been proposed and are currently in use. Conventional hitch assemblies typically include a rocker assembly for raising and lowering an implement coupled to the hitch, one or more hydraulic cylinders connected to the rocker assembly and a pair of draft links for mounting and pulling an implement. Such hitches also commonly include a third or upper link that cooperates with the rocker assembly and draft links to maintain a desired orientation of the implement.
The rocker assembly of conventional tractor hitches typically includes a rockshaft splined to receive rocker arms as well as a bell crank or lever for rotating the rockshaft in response to extension and retraction of a hydraulic cylinder. The rockshaft is supported on journal bearings either inboard or outboard of the rocker arms. For rear-mounted hitches, the rockshaft journal bearings are typically provided in a massive support casting secured to the upper, rear or side surfaces of the differential housing. For raising and lowering the hitch either a single or a pair of lift cylinders may be provided. Where a single lift cylinder is used, the cylinder is generally located within the differential housing and cooperates with a central bell crank or lever splined to the rockshaft to force rotation of the shaft and thereby to raise and lower the rocker arms. Where two lift cylinders are present, the cylinders are typically external to the differential housing and are mounted on either side of the rear differential. In both cases the rocker arms are connected to the draft links via lift links, including turn buckles for adjusting the distance between the rocker arms and draft links, and are raised and lowered by rotation of the rockshaft and rocker arms. Hitch assemblies generally of this type are described in U.S. Pat. No. 2,780,160, issued to Harris on Feb. 5, 1957; U.S. Pat. No. 3,310,123, issued to Abbott on Mar. 21, 1967; U.S. Pat. No. 4,470,613, issued to Sykes on Sept. 11, 1984; and U.S. Pat. No. 4,482,971, issued to Azzarello et al. on Sep. 5, 1989.
While such hitch assemblies have become generally reliable and useful tools for positioning implements carried by work vehicles, they are not without drawbacks, many of which stem from the structure of their rocker assemblies. For example, because the rockshaft and rocker arms are assembled as a unit, typically after the rockshaft is mounted in its support bearings, servicing of the bearings or assembly requires a time consuming process of dismantling and rebuilding the entire rocker assembly. Similarly, in hitches using a central bell crank and cylinder to rotate the rocker assembly, servicing of the cylinder requires partial dismantling of the differential as well as the rocker assembly. Moreover, because the rockshaft is generally supported by journal bearings inboard or outboard of the splines to which the rocker arms are attached, the rockshaft is subjected to considerable bending stresses, particularly when heavy implements are lifted on the hitch. This is particularly true for designs employing a central bell crank for rotating the rockshaft. However, even in hitches utilizing a pair of external lift cylinders coupled to the rocker arms, such stresses are high and can be increased by any misalignment between the rotational axis where each cylinder clevis joins the respective rocker arm and the rotational axis of the rockshaft.
There is a need therefore for an improved hitch rocker that is both rugged and relatively easy to mount and remove from the hitch assembly. In addition, there is a need for a hitch rocker that reduces the bending stresses in the rockshaft, while avoiding axis misalignment of the type tending to augment such stresses.